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From: Peter Xu <peterx@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: Tal Zussman <tz2294@columbia.edu>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Jason A. Donenfeld" <Jason@zx2c4.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,
	Pavel Emelyanov <xemul@parallels.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 2/3] userfaultfd: prevent unregistering VMAs through a different userfaultfd
Date: Fri, 6 Jun 2025 09:03:48 -0400	[thread overview]
Message-ID: <aELnNH5LTFHmtdfQ@x1.local> (raw)
In-Reply-To: <0a1dab1c-80d2-436f-857f-734d95939aec@redhat.com>

On Thu, Jun 05, 2025 at 11:06:38PM +0200, David Hildenbrand wrote:
> Not sure if relevant, but consider the following:
> 
> an app being controlled by another process using userfaultfd.
> 
> The app itself can "escape" uffd control of the other process by simply
> creating a userfaultfd and unregistering VMAs.

IMHO it's okay if it's intentional by the child. E.g., even after this
patch, the child, if intentional, can also mmap() a new VMA on top of the
uffd tracked region to stop being trapped by the parent.  The parent might
still get a UNMAP event if registered, but it'll not be able to track the
new VMAs mapped.

Thanks,

-- 
Peter Xu


  parent reply	other threads:[~2025-06-06 13:04 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-06-03 22:14 [PATCH 0/3] mm: userfaultfd: assorted fixes and cleanups Tal Zussman
2025-06-03 22:14 ` [PATCH 1/3] userfaultfd: correctly prevent registering VM_DROPPABLE regions Tal Zussman
2025-06-04 13:19   ` David Hildenbrand
2025-06-04 15:17   ` Peter Xu
2025-06-03 22:14 ` [PATCH 2/3] userfaultfd: prevent unregistering VMAs through a different userfaultfd Tal Zussman
2025-06-04  0:52   ` James Houghton
2025-06-05 20:56     ` Tal Zussman
2025-06-04 13:23   ` David Hildenbrand
2025-06-04 15:09     ` Peter Xu
2025-06-05 21:06       ` David Hildenbrand
2025-06-05 21:15         ` Tal Zussman
2025-06-06 13:03         ` Peter Xu [this message]
2025-06-06 13:15           ` David Hildenbrand
2025-06-05 21:11       ` Tal Zussman
2025-06-06 13:24         ` Peter Xu
2025-06-06 19:15           ` Tal Zussman
2025-06-05 21:06     ` Tal Zussman
2025-06-03 22:14 ` [PATCH 3/3] userfaultfd: remove UFFD_CLOEXEC, UFFD_NONBLOCK, and UFFD_FLAGS_SET Tal Zussman
2025-06-04 13:24   ` David Hildenbrand
2025-06-04 15:17   ` Peter Xu

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